This invention relates generally to electronic controls and, more particularly, to watchdog circuits for electronic controls.
Known watchdog circuits use charge holding capacitors to protect appliances or other devices. Typically, a microprocessor generates a pulse train signal on a designated watchdog pin. The pulse train signal charges the capacitor, either directly or indirectly. As long as the microprocessor generates the pulse train signal, the voltage across the capacitor remains between an upper and a lower threshold, and the watchdog circuit enables normal operation of the electronic control that is controlling the appliance or other device. If the microprocessor stops generating the pulse train signal, the voltage across the capacitor falls outside the thresholds, and the watchdog circuit disables normal operation of the electronic control. Known watchdog circuits use many components to keep the capacitor charged, thereby increasing the cost and decreasing the reliability of the circuit.
In one aspect, a method is provided for controlling an electronic control using a circuit that includes a damper capacitor. The method includes substantially discharging the damper capacitor and enabling operation of the electronic control when the damper capacitor is substantially discharged.
In another aspect, a method is provided for controlling an electronic control using a circuit that includes a damper capacitor. The method includes charging the damper capacitor and disabling operation of the electronic control when the damper capacitor is charged.
In another aspect, an appliance is provided that includes a watchdog circuit. The watchdog circuit includes a damper capacitor and an electronic appliance control that is electrically coupled to the watchdog circuit. The appliance control is operable when the damper capacitor is substantially discharged, and inoperable when the damper capacitor is charged.
In yet another aspect, a circuit is provided for controlling an electronic control. The circuit includes a damper capacitor and is configured to enable operation of the electronic control when the damper capacitor is substantially discharged, and disable operation of the electronic control when the damper capacitor is charged.
In a further aspect, a circuit is provided for controlling an electronic control. The circuit includes a damper capacitor and a damper reset transistor that is electrically coupled to the damper capacitor. The damper reset transistor has a first reset mode and a second reset mode, and is configured to substantially discharge when the damper reset transistor is in the first reset mode. The damper capacitor is configured to charge when the damper reset transistor is in the second reset mode. The circuit further includes an enable transistor that is electrically coupled to the damper capacitor and the electronic control. The enable transistor has a first enable mode and a second enable mode, and is configured to remain in the first enable mode when the damper capacitor is substantially discharged. The enable transistor is configured to remain in the second enable mode when the damper capacitor is charged. The circuit is configured to enable operation of the electronic control when the enable transistor is in the first enable mode, and disable operation of the electronic control when the enable transistor is in the second enable mode.